Field of the Invention
The present invention relates to a method for repairing a honeycomb core sandwich panel which is formed by sandwiching a honeycomb structured core between skins, and an apparatus for repairing the same.
Description of the Related Art
When an outer panel (skin) forming an outer surface of a fuselage or a wing of an aircraft is damaged by a lightning strike or a flying object such as hail, the outer panel needs to be repaired. To repair the outer panel, a composite material made of FRP (fiber reinforced plastics) or the like is used.
The composite material is fabricated by a method (wet lay-up) of impregnating fiber sheets with liquid thermosetting resin, laminating the fiber sheets, and curing the resin by heating, or a method of laminating semi-cured intermediate materials (prepregs), and curing the prepregs by heating. There is also a method of using a repair patch (a pre-cured patch) that is preliminarily thermally cured as the composite material, and bonding the repair patch to the outer panel by using a thermosetting adhesive.
The aircraft outer panel is formed by a lightweight and highly-rigid honeycomb core sandwich panel as well as metal and a composite material.
The honeycomb core sandwich panel is a panel having a structure in which a honeycomb structured core with a plurality of cells having a hexagonal cross section is held between skins.
In Japanese Patent Laid-Open No. 11-320724, a honeycomb core is fabricated by using gappy FRP obtained by impregnating with resin a fiber base material where a gap is formed between woven fibers. Since partition walls between cells of the core have breathability, gas produced in thermal-curing of an adhesive for bonding skins to the honeycomb core can be released outside (degased).
When the honeycomb core sandwich panel is repaired, it is necessary to cure the thermosetting resin contained in the composite material by heating the composite material by a heating device.
To reliably cure the thermosetting resin at the time of heating, the panel is maintained at a high temperature for a predetermined time. Moisture accumulated in the cells or on the partition walls of the core of the panel thereby becomes water vapor to generate a high pressure within the cells. The panel may be destroyed by the water vapor pressure.
When the core in which the partition walls between the cells have breathability as in Japanese Patent Laid-Open No. 11-320724 is employed, the water vapor pressure can be reduced to some extent. However, the panel cannot be reliably prevented from being destroyed. Moreover, it is difficult to fabricate the core as described above, and such the core results in a high cost.
Therefore, to reliably prevent the panel from being destroyed at the time of repair, a drying step of sufficiently drying the core to eliminate water is performed before heating. It thus takes a very long time to repair the panel.
An object of the present invention is to reduce a time required for repairing the honeycomb core sandwich panel.